Gas turbines are employed in many fields for driving generators or operational machines. In this case, the energy content of a fuel is used to generate a rotational motion of a turbine shaft. For this purpose, the fuel is burnt in a combustion chamber, compressed air being supplied by an air compressor. The working medium, which is generated in the combustion chamber by the combustion of the fuel and which is at high pressure and high temperature, is then guided via a turbine unit connected downstream of the combustion chamber and expands, while performing work, in this turbine unit.
In order to generate the rotational motion of the turbine shaft, a number of turbine blades are arranged on the turbine shaft. These blades are usually combined into blade groups or blade rows and drive the turbine shaft via a transfer of momentum from the flow medium. In order to conduct the flow medium within the turbine unit, furthermore, guide vane rows connected to the turbine casing are usually arranged between adjacent rows of turbine blades. In this arrangement, the turbine blades/vanes, in particular the guide vanes, usually have a profiled blade/vane aerofoil extending along a blade/vane axis for the appropriate conduction of the working medium. In order to fasten the turbine blade/vane to the respective support body, a platform extending transversely to the blade/vane axis and embodied as an engagement base is integrally formed at the end of the blade/vane aerofoil.
In order to achieve a particularly favorable efficiency, such gas turbines are usually designed, for thermodynamic reasons, for particularly high outlet temperatures—approximately 1200° C. to approximately 1300° C.—of the working medium flowing out of the combustion chamber and into the turbine unit. With such high temperatures, the components of the gas turbine, in particular the turbine blades/vanes, are subjected to comparatively high thermal loading. In order to ensure a high degree of reliability and a long life of the respective components, even under such operating conditions, the components affected are usually embodied in such a way that they can be cooled.
In consequence, the turbine blades/vanes are usually embodied as so-called hollow profiles in modern gas turbines. For this purpose, the profiled blade/vane aerofoil has cavities, also referred to as blade/vane core, in its interior region; a coolant can be conducted within these cavities. Exposure of the thermally particularly loaded regions of the respective blade/vane aerofoil to coolant is made possible by the coolant ducts formed in this way. In this arrangement, a particularly favorable cooling effect, and therefore a particularly high level of operational reliability, can be achieved by the coolant ducts taking up a comparatively large spatial region within the respective blade/vane aerofoil and by the coolant being conducted as close as possible to the respective surface exposed to the hot gas. On the other hand, in order to ensure adequate mechanical stability and load-carrying capability in such a configuration, the respective turbine blade/vane can have flow through it in a plurality of ducts, a plurality of coolant ducts. These ducts can be exposed to coolant and are respectively separated from one another by comparatively thin separating walls, being provided within the blade/vane profile.
For efficiency reasons, it can be desirable to design such a turbine blade/vane for a comparatively low consumption of coolant. It is precisely in the case where the turbine blade/vane is exposed to comparatively hot working medium that reliable cooling of the individual components of the turbine blade/vane with only limited consumption of coolant can often only be achieved by way of a comparatively thin-walled embodiment of the individual components, with a comparatively small amount of material being required. It is precisely the thermal stresses produced in individual components of the turbine blade/vane during operation of the gas turbine and the substantial mechanical loading which likewise occurs, which can lead to material fatigue or even material fracture. This may require the use, which is actually undesirable, of comparatively thick-walled structural parts, for which a correspondingly complicated cooling system with correspondingly increased supply of coolant then has to be made available.